Change PhetioCapsule phetioType to phetioValueType

[pixelzoom]

Should PhetioCapsule API be changed from phetioType to phetioValueType, as was done for DerivedProperty?

Example in PhetMenu.ts:

    const aboutDialogCapsule = new PhetioCapsule( ..., {
      ...
      phetioType: PhetioCapsule.PhetioCapsuleIO( Dialog.DialogIO )
    } );

The PhetioCapsule.PhetioCapsuleIO bit is required in all cases. So why not change to:

-      phetioType: PhetioCapsule.PhetioCapsuleIO( Dialog.DialogIO )
+      phetioValueType: Dialog.DialogIO

[samreid]

Adding to https://github.com/phetsims/phet-io/issues/1914 and self-unassigning.